On Nov 14, 2007 11:32 -0500, Chuck Lever wrote: > I disagree: we don't need a "bullet-proof" log. We can get a significant > performance improvement even with a permanent dnotify log implemented in > user-space. We already have well-defined fallback behavior if such a log > is missing or incomplete. > > The problem with a permanent inotify log is that it can become unmanageably > enormous, and a performance problem to boot. Recording at that level of > detail makes it more likely that the logger won't be able to keep up with > file system activity. > > A lightweight solution gets us most of the way there, is simple to > implement, and doesn't introduce many new issues. As long as it can tell > us precisely where the holes are, it shouldn't be a problem. Jan Kara is working on a patch for ext4 which would store a recursive timestamp for each directory that gives the latest time that a file in that directory was modified. ZFS has a similar mechanism by virtue of doing full-tree updates during COW of all the metadata blocks and storing the most recent transaction number in each block. I suspect btrfs could do the same thing easily. That would allow recursive-descent filesystem traversal to be much more efficient because whole chunks of the filesystem tree can be ignored during scans. Cheers, Andreas -- Andreas Dilger Sr. Software Engineer, Lustre Group Sun Microsystems of Canada, Inc. - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
